Short-circuiting device



Nov. 12, 1929. E. J. HAVERSTICK 3 ,11

SHORT CIRCUITING DEVICE Filed May ;9z7

Fly. i,

INVENTOR Earl J Ha versf/c/r ATTORNEY Patented Nov. 12, 1929 UNITEDSTATES PATENT OFFICE EARL J. HAVERSTICK, OF OAKMONT, PENNSYLVANIA,ASSIGNOR T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATIONOF PENNSYLVANIA SHORT-CIRCUITING DEVICE Application filed May 19,

My invention relates to circuit-making and breaking devices andspecifically to short-circuiting devices for series lighting circuits orthe like and is a continuation in part of my copending applicationSerial No. 151,692, filed November 30, 1926, and assigned to theWVestinghouse Electric and Manufacturing Company.

One object of my invention is to provide means for effectivelyshort-circuiting a lamp or other device in case of an interruption ofthe circuit through the lamp.

A second object of my invention is to provide a cutout that willreliably breakdown at a comparatively low voltage. v

Another object of my invention is to provide a device of theabove-indicated character having means embodied therein for regulatingthe voltage at which breakdown will occur.

Another object of my invention is to provide a cutout such that ordinaryvariations in operating temperatures will not materially change thevalue of the breakdown voltage.

A further object of my invention is to provide a cutout that will notshort-circuit through the device when subjected to a surge caused by therelease of bound charges in a line, such as a lightning stroke.

Heretofore, devices for similar purposes that operated at comparativelyhigh voltages have been used, but such devices were not suitable forcircuits of less than about 350 volts. Such devices were thoseconsisting of a varnished fabric inserted between two electrodes. Thefabric would puncture and establish contact between the electrodes at acomparatively high voltage and was useful only in a higl1-voltagecircuit. Furthermore, it could not be made to regulate closely thevoltage at which breakdown occurred in operating conditions.

My invention provides a device'that may be made to operate at arelatively low voltage, such as 50 volts. The value at which thebreakdown will occur may be closely regulated, and changes intemperature on account of varying operating conditions do not materiallyaffect the breakdown voltage.

4 When graphite is placed between the elec- 1927. Serial No. 192,557.

trodes of different potential a leakage will occur. I have found that iftwo discs about one-half inch in diameter are used as electrodes, and apaper spacer which is coated with graphite and provided with a 3/64 inchopening is disposed between the two discs or electrodes, a'leakage ofthe order of one milliampere will occur when the potential between theelectrodes is 25 to 30 volts. I have found upon increasing the voltagethat the leakage increases. With the increase in leakage, the graphiteconducts a small but a slightly increased amount of current and iswarmed thereby.

Since graphite has a negative temperature coclficient of resistance, theconductivity will increase directly as the temperature. Consequentlyfurther increases in current will continuously increase the temperatureand conductivity of the graphite more and more. It is believed that thecumulative efiects of temperature and conductivity mutually increasewith the increased voltage until a conducting medium suflicient to causea breakdown between the plates is formed in the opening and in thestructure enveloping the same. When even a slight rupture occurs anamount of current suflicient in many instances to form a metallic pathbetween the two electrodes will almost instantly result in a completeshort circuiting of the electrodes. The complete operation of heatingand short circuiting usually occurs in about a half cycle.

I have discovered that the breakdown voltage for a spacer havingopenings or apertures coated with graphite is influenced by the specificgravity of the graphitic liquid used for coating the spacer and by thethickness of the spacer and by the type of material used in making thespacer. I have found that the breakdown Voltage increases with adecrease of the specific gravity of the coating liquid. When the liquidis too concentrated, it results in an erratic behaviour of the device. Iprefer to use a specific gravity of about 1.035, although variations inthe specific gravity of the graphite suspension can be utilized withsuccess.

I have found that an increase in thickness of spacer results in acorresponding increase material.

in the breakdown voltage. I prefer to limit the thickness of the spacerto 3 to 10 mils for low voltage series lighting service. The type ofpaper used influences the breakdown voltage. The coating solution willpenetrate a porous paper more completely than it will non-porous orimpervious paper, and m N graphite will be distributed throughout theorous paper and on the surface thereof. Vhen porous paper is coated withthe graphite suspension, the structure is apt to be flaky and thecoating lacks adherence. A greater leakage and a lower breakdown voltagewill be required for a porous impregnated paper than for a coatedimpervious paper of equal thickness. Since the leakage of current isgreater and the breakdown voltage is smaller and less constant withincreasing amounts of graphite between the plates, I prefer for mostpurposes to utilize a non-porous paper upon which the coating ofgraphite can be easily regulated and the leakage limited largely to thesurface coating.

The breakdown voltage may be controlled by increasing and decreasing thesize of the opening. I prefer to utilize openings of 3/ to 3/ 16 inch indiameter. Within these limits there is a variation in breakdown voltageof approximately volts.

I have found that a most efficient means of controlling the breakdownvoltage is to vary the thickness of the washer and the specific gravityof the graphite coating solution.

If the breakdown voltage of one cut-out disc is too low, the breakdownvoltage may be increased by inserting a plurality of the treated'paperdiscs between the terminals, the breakdown voltage being variedaccording to the number of discs employed.

My invention may best be understood by reference to the accompanyingdrawings, in which,

Figure 1 shows a greatly enlarged exploded sectional view of onemodification of my .shortcircuiting device,

Fig. 2 shows a similar view of another modification of my device, and

Fig. 3 is a diagrammatic view showing a preferred manner of utilizing myinvention.

The preferred form of my invention is shown in Fig. 1. Two conductingplates, 1 and 2, of aluminum or other electrically con ducting materialare separated by a perforat ed Washer-like spacer 3 of mica, asbestos,cloth, paper or other similar non-conducting I have found a closegrained or substantially impervious paper to be the most satisfactoryfor use as a spacer material. As previously stated, the paper disc has adiameter of the order of one-half inch and a thickness of the order of 3to mils. 1111 opening 4 about 3/64 of an inch in diamet r, is providedin the disc, and the upper surface 5 and the opening 4 are coated withgraphite 6. The

age to the lamps.

graphite also covers a portion 7 of the lower side of the spacer 3, thusproviding a contact with plate 2.

In making the type of cut-out described above, I prefer to use a stripof paper of suitable width and punch the holes at along the strip at adistance of about 3/4 inch apart. The strip of paper is then dampenedand coated with water suspension of graphite, such as aquadag of aspecific gravity of about 1.035. Discs of the desired dimensions, eachhaving an aperture at its center, are then punched from the strip. Ihave found that aquadag is the most suitable conducting material, butthat other materials of a similar nature, such as a metallic paint, wlich consists of metal particles suspended in a vehicle, printers ink orindia ink, may be used. The edge of the spacer is coated with a suitableadhesive material, such as shellac, and the two aluminum electrodes arethen placed on either side of the spacer and electrical contact ofgraphite and electrodes is secured by pressing the discs and spacertogether, thus forming a unitary structure. An alternative method ofconstructing the apertured disc is to coat a strip of paper, or thelike, with a solution of aquadag and punch the apertures and discs outof the strip while the strip is supported on a soft block, so that theaquadag will be forced through the opening and caused to coat themargins thereof.

Another modification of my device is shown in Fig. 2. The spacer 13 is adisc of cloth, having threads 14, paper or the like, the fine openingsof which form the apertures in which the graphite 15 is placed. In orderto coat the cloth and to obtain .a material which will be integral withthe cloth, I prefer to use a suspension of graphite in water of about1.035 specific gravity. The out-out device 15 assembled by placing thetreated cloth be tween the plates 1 and 2, coating the edges withshellac and applying pressure as before.

My invention may be utilized in lamps that are associated with aconstant current series lighting system, as shown in Fig. 3. Forexample, lamps, 21, 22,23 and 24 normally operating at volts, areconnected in a branch line 25 through series transformers 26, 27, 28 and29. Tl e branch line may be connected to the secondary winding of aconstant current transformer 32, the primary winding 33 of which isconnected across the main line 34 and 35. The cut-out devices 36, 37, 38and 39 are placed in the secondary branch line circuits across theterminals of the lamps 21, 22, 23 and 24:.

The lamp transformers 26, 27, 28 and 29 are so proportioned as todeliver the proper volt- W'hcn an interruption such as the rupture ofthe filament of lamp 21 oc curs, the voltage of thesecondary branch line40 across the terminals of the eutout device increases until the cut-out'36 breaks down and short-circuits the lamp 21 and the secondary windingof the transformer 26. Thus, the cut-out prevents the voltage across theterminals of the secondary winding of the transformer from rising to adestructive amount as the breakdown reduces the voltage to substantiallyzero.

When using a graphite suspension of a given specific gravity, thevoltage at which breakdown will occur may be increased by using athicker spacer or a smaller opening or both. Conversely, if the spaceris made thinner, or the opening is made larger, the breakdown voltagewill be decreased.

The breakdown voltage of the second modification of my device may becontrolled by increasing or decreasing the thickness of the cloth, byvarying the specific gravity of the suspension of graphite and byvarying the porosity of the cloth or spacer.

I have found that a discharge occasioned by the release of a boundcharge, such as lightning, does not rupture the cut-out devices which Ihave described and that the device may be made susceptible to breakdownvoltages approximately 50 volts, although the breakdown voltage may bevaried at Wlll.

Other materials than graphite may be used to make the covering of thespacer provided that the coating produced on the spacer has an extremelysmall conductivity. Such a material as boron which has a negativetemperature coefficient of resistance, and powdered gums and resinswhich likewise provide a small leakage and have a negative temperaturecoeflicient of resistance may be substituted for the graphite and usedalone or in conjunction with other materials of greater or lessconductivity.

It is to be understood that the device which I have shown and described,and its utility in connection with lighting devices is illustrative ofmy invention and that modifications may be made therein, withoutdeparting from the spirit and scope of my invention as defined in theappended claims.

I claim as my invention:

1. A circuit closing device comprising a plurality of conducting bodies,an apertured spacer disposed therebetween and particles of a materialhaving a small conductivity disposed on the margin of said aperture andsurrounding said aperture on both the top and bottom surfaces of saidspacer.

2. A circuitclosing device comprising a plurality of conducting bodies,an apertured spacer disposed therebetween and particles of materialhaving a negative coefiicient of resistance disposed in said a ertureand surrounding said aperture on both the top and bottom surfaces ofsaid spacer.

3. A circuit closing device comprising a. plurality of conductingbodies, an apertured spacer disposed therebetween and particles ofcarbon disposed on the edge of said aperture and surrounding saidaperture on both the top and the bottom surfaces of said spacer.

4. A circuit closing device comprisin a plurality of conduction bodies,a high resistance spacer having a thickness of 3 to 10 mils disposedtherebetween and particles of graph ite disposed on an edge of saidspacer and on the top and bottom surfaces of said spacer immediatelyadjacent to said edge.

5. A circuit closing device comprising a plurality of conducting bodies,an apertured spacer disposed therebetween and graphite disposed in saidaperture and surrounding said aperture on both the top and bottomsurfaces of said spacer to form a high resistance leakage path betweenthe conducting bodies.

6. The method of making a circuit closing device comprising cuttingapertures in a sheet of spacing material, coating the sheet of spacingmaterial with a graphitic carbon, cutting a disk from the sheet, havingan aperture therein, coating the edge of the disk with adhesivematerial, placing conducting bodies, one on each side of the disk, andapplying pressure.

7. The method of making a circuit closing device comprising cutting anaperture in a sheet of spacing material and applying a coating of ahigh-resistance material to one side of the sheet in such manner thatthe coating adheres to the edges of the aperture and to a small portionof the other side of the sheet immediately surrounding said aperture.

In testimony whereof, I have hereunto subscribed my name this 10th dayof May, 1927.

EARL J. HAVERSTICK.

